Periodically modify a JavaFX StackedBarChart CategoryAxis - charts

Question

I'm trying to find a way to update the Categories of a JavaFX CategoryAxis(). I made an observable list of the categories and they also do update in the plot() function. However, if I try to add a new item to the series, I get a java.lang.IllegalStateException. Although I know, that not a state is causing the error, moreover the dynamic adding seems to be the problem. Below I attached my Code.
package application;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import javafx.animation.Animation;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.chart.CategoryAxis;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.StackedBarChart;
import javafx.scene.chart.XYChart;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import javafx.util.Duration;
public class Main extends Application {
final XYChart.Series series1 = new XYChart.Series();
final XYChart.Series series2 = new XYChart.Series();
ObservableList<XYChart.Data> xyList1 = FXCollections.observableArrayList();
ObservableList<XYChart.Data> xyList2 = FXCollections.observableArrayList();
ObservableList<String> myXaxis = FXCollections.observableArrayList();
int i;
#Override public void start(Stage stage) {
stage.setTitle("Line Chart Sample");
final CategoryAxis xAxis = new CategoryAxis();
final NumberAxis yAxis = new NumberAxis();
xAxis.setLabel("Month");
final StackedBarChart<String,Number> lineChart =
new StackedBarChart<String,Number>(xAxis,yAxis);
lineChart.setTitle("Woohoo, 2010");
lineChart.setAnimated(false);
series1.setName("Test 1");
series2.setName("test 2");
Timer timer = new Timer();
timer.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
plot();
}
}, 0, 1000);
Scene scene = new Scene(lineChart,800,600);
xAxis.setCategories(myXaxis);
XYChart.Series XYSeries1 = new XYChart.Series(xyList1);
XYChart.Series XYSeries2 = new XYChart.Series(xyList2);
lineChart.getData().addAll(XYSeries1,XYSeries2);
i = 0;
stage.setScene(scene);
stage.show();
}
public void plot() {
SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
Date date = new Date();
date.setTime(date.getTime() + i++ * 11111);
myXaxis.add(dateFormat.format(date));
System.out.println(myXaxis);
// with the line below uncommented the application breaks. Without the x-axis is updated as intended.
//xyList1.add(new XYChart.Data(dateFormat.format(date), Math.random()*10));
}
public static void main(String[] args) {
launch(args);
}
}

Answer 1

Issue - Transitive Modification of Scene Graph Nodes off of the JavaFX Application Thread
Don't modify scene nodes (or even observable lists of data on which scene nodes depend), off of the main JavaFX application thread (it's illegal - as the IllegalStateException you received states).
A Timer thread does not run things on the JavaFX application thread.
Potential Fixes
There are a few ways to fix this:
Continue using a Timer, but surround the plot() call in the timer with Platform.runLater.
Use the JavaFX animation framework (the Timeline), which always runs all of it's code on the JavaFX application thread.
Of the two options, I think I'd prefer the second, but either will work.
Timer style solution
Timer timer = new Timer();
timer.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
Platform.runLater(new Runnable() {
#Override public void run() {
plot();
}
});
}
}, 0, 1000);
Timeline style solution
Timeline timeline = new Timeline(
new KeyFrame(
Duration.ZERO,
new EventHandler<ActionEvent>() {
#Override public void handle(ActionEvent actionEvent) {
plot();
}
}
),
new KeyFrame(
Duration.seconds(1)
)
);
timeline.setCycleCount(Timeline.INDEFINITE);
timeline.play();
Alternative Service based solution
I suggest that you read up on concurrency in JavaFX.
Another alternative would be to use Task or Service in conjunction with a ScheduledExecutorService and updates running via Platform.runLater(). However this kind of solution, while sophisticated and flexible, is more complicated than the problem warrants as you described it and the simple Timeline or Timer based solutions should be preferred. The more complicated Service based solution is appropriate if each pulse results in the execution of a time consuming algorithm or a lot of network or file based I/O.